This invention relates to progressing-cavity-type positive displacement helical pumps for handling liquid and comminuted material, such as the progressing cavity helical pump of my U.S. Pat. Nos. 3,512,904 and 3,938,744. More particularly, the invention relates to an improved flexible coupling shaft of the type that extends through a helical pump rotor of tubular form and flexes therein for coupling the pump rotor to a rotary drive shaft to accommodate orbital movement of the rotor during rotation thereof.
Progressing-cavity-type positive displacement rotary devices of the general class that includes the devices disclosed in my U.S. Pat. Nos. 3,512,904 and 3,938,744 (hereinafter referred to as "Allen" devices or pumps) have a rotor with an exterior helical surface that engages the surrounding interior helical surface of the stator, the rotor surface having one more thread than the stator surface and a lead twice that of the stator surface. Thus, the stator surface and the rotor surface define therebetween sealed pumping cavities that are axially advanced as the rotor rotates and at the same time orbits in the same direction at two or more times the rate of its rotation. For a more complete description of Allen pumps of this type, reference is made to my aforesaid U.S. Pat. No. 3,512,904.
This class of rotary helical devices differs from the well-known Moineau-type devices as disclosed, for example, in U.S. Pat. No. 1,892,217. In the Moineau-type device, the helical rotor orbits in the reverse direction relative to its rotation and the helical stator surface has one more thread than the helical rotor. The coupling between the Moineau rotor and drive shaft must utilize a universal connection to accommodate the orbital motion of the rotor, the orbital speed being equal to the speed of rotation. Various types of universal connections or couplings have been utilized, including conventional universal joints, long flexible shafts, etc.
Typical examples of such couplings utilizing flexible shafts, or the like, are described in U.S. Pat. Nos. 2,028,407; 2,456,227; and 3,612,734 and in British Pat. No. 1,379,907. The devices shown use flexible metal shafts or metal cables. The flexing produces substantial stresses in the metal shafts or cables and the devices are prone to failure due to fatigue.
Among the many applications for Allen pumps are certain uses where relatively small units are used to pump slurries, such as sludge from dust separators, and thick, viscuous industrial chemical products. It is desirable that these pump units be of compact, easily maintained construction and that replacement of parts, such as a worn rotor or stator, be easily accomplished.
One advantageous form of flexible coupling is disclosed in my U.S. Pat. No. 3,938,744 wherein the pump is designed primarily for use in the pumping of sewage. The same drive shaft that drives the pump rotor is used to drive a grinding unit that operates simultaneously with the pump. In that application, the shaft extends through a hollow rotor and the coupling between the rotor and the shaft is accomplished by a flexible sleeve positioned within the rotor and surrounding the drive shaft. The flexible sleeve is connected at one end to the shaft and at the opposite end to the rotor. That construction is especially adapted to applications where the drive shaft extends completely through the rotor, whereas, the present invention deals with applications wherein there is no need for the drive shaft to extend through the rotor.
More specifically, the present invention is concerned with the flexible connection or coupling between the rotary drive shaft and a generally hollow orbital rotor of the type shown in my U.S. Pat. No. 3,938,744, the required flexibility being provided by a flexible coupling shaft with at least a portion of its length being adapted to flex in the space within the hollow rotor. The connection of the flexible shaft to the rotor can be accomplished in several conventional ways, although these usually require relatively large components, such as hubs, flanges, etc., which require considerable space relative to the rotor and shaft. While sufficient space may be available in larger pumps, there is frequently insufficient space in the case of smaller, lower capacity pumps. Also, the smaller the pump, the more difficult and time-consuming the assembly of the connection between the hollow rotor and flexible shaft becomes.
Another related problem in the field of liquid pumps generally, as well as progressing-cavity-type pumps of the type described above, is that of preventing leakage of the material being pumped along the drive shaft to the shaft bearings. Generally, this is done by providing a packing gland between an outer portion of the shaft and a surrounding bore in the housing. This packing must not only be adequately retained in its desired position, but must be periodically replaced. In the past, the removal and replacement has required substantial disassembly of the pump and has been a burdensome, time-consuming procedure.
The device of the present invention satisfies the requirements and difficulties indicated above and affords other features and advantages heretofore not obtainable.